The present invention relates to a method and a system for anti creep operation for an automatic transmission, and more particularly relates to such a method and such a system, in which anti creep action of the transmission is provided by observing whether certain anti creep conditions are holding, and by providing a certain time delay after observing of the occurrence of holding of said anti creep conditions, before actual performing of anti creep action.
The present invention has been described in Japanese Patent Application Ser. No. 60-223355 (1985), filed by an applicant the same as the entity assigned or owed duty of assignment of the present patent application; and the present patent application hereby incorporates into itself by reference the text of said Japanese Patent Application and the claim and the drawings thereof; a copy is appended to the present application. Further, the present inventors wish hereby to attract the attention of the examining authorities to copending patent applications Ser. Nos. 868,513 now U.S. Pat. No. 4,730,708; which may be considered to be material to the examination of the present patent application.
There is a conventional type of automatic transmission for a vehicle which comprises a fluid torque converter which receives at its power input shaft a supply of rotational power from a crank shaft or the like of an internal combustion engine and which transmits said power from its power output shaft with a certain degree of torque amplification and with a certain degree of slippage to a gear transmission mechanism which can selectively provide any one of a plurality of forward speed stages (gearing ratios) between its power input shaft thus connected to said power output shaft of said torque converter and its power output shaft connected to the driven road wheels of the vehicle so as to transmit rotational power thereto. Such a torque converter provides an amount of torque amplification and an amount of slippage between its power input shaft and its power output shaft both of which vary as the rotational speed of the input member (or pump impeller) of said torque converter varies and the load on the power output member (or turbine member) of said torque converter varies, according to determinate performance characteristics of said torque converter. And the gear transmission mechanism, which typically comprises a plurality of selectively engagable gear trains, is set in a determinate way to one or the other of said plurality of forward speed stages, according to the current values of various operational parameters of the internal combustion engine and of the vehicle incorporating it, said operational parameters including but not being limited to engine load (usually taken as being represented by engine throttle opening amount), vehicle road speed, and the one of various shift ranges such as "D" or drive range, "S" or second range, and "L" or low range which is currently selected on a manually controlled range selection means provided to the vehicle. And the manner in which said plurality of forward speed stages is thus selected between according to the current values of said vehicle operational parameters is conventionally described by one or more shift diagrams, typically one for each one of such forward shift ranges which encompasses more than one speed stage.
When the abovementioned manual range setting means is set to "D" or drive range or some other forward driving range and the vehicle speed is substantially zero, i.e. the vehicle is substantially at rest, and further the internal combustion engine is substantially idling: then, in view of the desirability of maintaining a capability for relatively rapid starting off of the vehicle from this stopped condition, it is usually practiced not to put the gear transmission mechanism into a neutral condition in which it is incapable of transmitting rotational power between its power input shaft and its power output shaft, but instead typically said gear transmission mechanism is left as engaged to its first speed stage, i.e. its speed stage in which it provides a maximum reduction gearing ratio between its power input shaft and its power output shaft. Thereby a rapid response is available when the accelerator pedal of the vehicle is pressed in order to move off from rest, and the transmission is maintained in a state ready to transmit rotational power from the engine to the wheels of the vehicle, with the torque converter providing relatively great slippage and transmitting a relatively small amount of torque at this time due to the relatively low rotational speed of its power input member which is being driven by the internal combustion engine which is idling. When the accelerator pedal is in fact thus depressed by the foot of the vehicle driver, the rotational speed of the power output member of the engine (typically its crank shaft) rises, and accordingly the rotational speed of the power input member of the torque converter rises, and thereby the torque converter is caused to transmit substantially more torque, i.e. to provide less slippage between its power input member and its power output member. This increased torque is immediately transmitted by the gear transmission mechanism, since it is being maintained as engaged to its first speed stage as explained above, to the driven road wheels of the vehicle; and thereby the vehicle is caused to move off from rest.
This leaving of the gear transmission mechanism engaged to its first speed stage during the engine idling vehicle stopped condition produces the consequence of being liable to still transmit some substantial amount of torque from the torque converter through said gear transmission mechanism to the driven road wheels of the vehicle at this time. If not counteracted, this produces so called creep of the vehicle, and indirectly leads to engine idling vibration. Further, it becomes necessary for the driver of the vehicle to press relatively hard on the brakes of the vehicle while the vehicle is thus stopped, as for example at a traffic light or the like, in order positively to prevent forward motion of the vehicle. And the drag of the torque converter on the internal combustion engine causes the fuel economy of the engine to be bad, and furthermore the transmission fluid in said torque converter tends to become hot, which can in some cases lead to an overall overheating problem for the vehicle as a whole. Accordingly, various types of anti creep control have been proposed, and implemented, for such automatic transmission systems.
This type of gear transmission mechanism typically includes a clutch which is generally called a forward clutch which is engaged when and only when the gear transmission mechanism is engaged to one of its forward speed stages, i.e. is providing forward driving to the vehicle. This forward clutch typically comprises two sets of friction elements connected to the two members which it selectively engages together, and is typically actuated by said two sets of friction elements being pressed together by a hydraulic servo device which has a pressure chamber for its actuation. Thus, the forward clutch is engaged when hydraulic fluid pressure is supplied to said pressure chamber of said hydraulic servo device thereof, with the engagement pressure between said sets of friction elements of said clutch and accordingly its torque transmission capability increasing the greater is the pressure value of said hydraulic fluid pressure. Accordingly, the assignee of the present patent application, who is also the applicant of the Japanese patent application of which the priority is being claimed for the present application, has proposed - in, for example, Japanese Patent Applications Ser. Nos. 41-18128 (1966), 56-117742 ( 1981), 57-10444 (1982), 57-75829 (1982), 57-115087 (1982), and 59-176300 (1984), the first of which has been published as Japanese Patent Publication Ser. No. 47-19962 (1972), and the next listed ones of which have been respectively laid open as Japanese Patent Lying Open Publications Ser. Nos. 56-21047 (1981), 58-128552 (1983), 58-193953 (1983), and 59-6454 (1984), and none of which is it intended hereby to admit as prior art to the present patent application except to the extent otherwise required by applicable law - that, in the above described condition when the engine of the vehicle is substantially in the idling condition and the vehicle speed is substantially zero, the hydraulic fluid pressure, which is thus being supplied as an actuating pressure to a frictional engaging device of the gear transmission mechanism which is of the so called forward clutch type which is engaged when and only when the gear transmission mechanism is engaged to one of its forward speed stages, should be substantially decreased. Doing this allows said forward clutch to slip somewhat during this engine idling vehicle stopped operational condition, and desirably this actuating pressure for the forward clutch is in fact so reduced as to be just at the upper level that still ensures that the gear transmission mechanism no longer transmits torque to any substantial extent while the vehicle is stopped. This means that substantially no vehicle creep takes place, and thus there is no requirement for the driver to press on the vehicle brake in order to maintain the vehicle in the stationary state. Further, the occurrence of idling vibration is made much less likely. The fuel economy of the vehicle is also improved. Also, since there is substantially less churning up of the transmission hydraulic fluid in the fluid torque converter, the problem of heating up of said torque converter is substantially overcome. The actuating pressure for the forward clutch can be quickly raised to an appropriate operational level when the accelerator pedal of the vehicle is depressed in order to start off the vehicle from rest, and so the provision of this anti creep device does not make the obtaining of a good response for starting off the vehicle much more difficult. Alternatively, as suggested in the specifications and drawings of Japanese Patent Application Ser. No. 59-176300 (1984), and in Japanese Patent Laying Open Publication Ser. No. 57-42243 (1982), it is possible to set the gear transmission mechanism of the transmission to a higher speed stage during the provision of anti creep action for the transmission.
A problem that has occurred with such a system is as follows. In the above outlined constructions and methods, during the prevalence of the conditions for providing anti creep action, which are typically when the engine of the vehicle is substantially in the idling condition and the vehicle speed is substantially zero, either (in the first type of case discussed above) the actuating hydraulic fluid pressure for the forward clutch is ideally reduced to a so-called waiting valve, which should be as high as possible short of causing said forward clutch to provide substantial torque transmission, so that said forward clutch is ready to be rapidly returned to the engaged state by moderate increase of said actuating pressure, or (in the second type of case discussed above) the gear transmission mechanism of the transmission is set to its aforesaid speed stage higher than its first speed stage. In either case, thus, anti creep action is provided for the transmission, when and only when the conditions therefor, i.e. the condition that the engine of the vehicle is substantially in the idling condition and the condition that the vehicle speed is substantially zero, are prevailing.
However, this rather over simplistic method of operation is not entirely satisfactory. Since anti creep control is performed as soon as the conditions therefor start to be prevailing, thus, in the operational circumstances when said anti creep conditions only hold momentarily, the so called hunting phenomenon occurs. In the first type of case discussed above, this causes the forward clutch to be rapidly engaged and disengaged, so that repeated clutch engagement shock is caused and the service life of the transmission is inevitably shortened. In the second type of case discussed above, the gear transmission mechanism of the transmission is repeatedly set to its aforesaid speed stage higher than its first speed stage, and then back to its first speed stage, thus causing repeated speed stage engagement shock and again inevitably shortening the service life of the transmission.
Because of all this, there has been proposed, in Japanese Patent Laying Open Publication Ser. No. 59-34050 (1984), which it is not intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law, the concept of providing anti creep control of a vehicle transmission, in which the occurrence of said conditions for providing anti creep action, i.e. that the engine of the vehicle is substantially in the idling condition and the vehicle speed is substantially zero, is detected, and in which the anti creep control is only performed, if said conditions have persisted throughout a certain time period.
With this method for anti creep control, the above outlined hunting problem is indeed solved, but, if first the conditions for providing anti creep control start to prevail, and then before the elapsing of the above identified determinate time period said anti creep provision conditions stop prevailing, then the time elapsed so far is canceled, and upon the prevailing again of the anti creep conditions the timing is again recommenced. Accordingly, in some conditions of staccato prevailing and not prevailing of the anti creep conditions, the start of the actual provision of anti creep action can become unduly delayed.